1. Field of the Invention
This invention relates to an improved industrial process for the preparation of 4-methoxy-2,2',6'-trimethyldiphenylamine useful as an intermediate for the production of a color-forming agent for heat-sensitive or pressure-sensitive recording papers.
2. Description of the Related Art
4-Methoxy-2,2',6'-trimethyldiphenylamine has heretofore been prepared by dehydrobromination and deacylation of an acetylation product of 2-methyl-4-methoxyaniline and 2,6-dimethylbromobenzene or of 1-bromo-4-methoxy-2-methylbenzene and an acetylation product of 2,6-dimethylaniline.
These conventional processes are, however, accompanied by drawbacks such as complex reaction steps and a low reaction velocity. With a view toward overcoming such drawbacks, the present inventors previously proposed a process for the preparation of 4-methoxy-2,2',6'-trimethyldiphenylamine in which 2,6-dimethylphenol is used as a hydrogen acceptor. While forming 2,6-dimethylhexanone in the reaction system, 2,6-dimethylcyclohexanone is reacted with 2-methyl-4-methoxyaniline in the presence of a hydrogen transfer catalyst to prepare 4-methoxy-2,2',6'-trimethyldiphenylamine (Japanese Patent Laid-Open No. 193949/1985, U.S. Pat. No. 4,804,783). Although this process has simplified the reaction steps and improved the reaction velocity, the process cannot be considered as an industrially satisfactory process, because the process has a drawback such as poor selectivity to 4-methoxy-2,2',6'-trimethyldiphenylamine. Accordingly, there is still need for further improvement in the process.